1. Field of the Invention
This invention relates generally to high-bandwidth digital content protection (HDCP) transmission systems and relates more particularly to optical fiber links with waveguide combiners or splitters.
2. Description of the Related Art
High-bandwidth digital content protection (HDCP) is a specification developed by Intel Corporation to protect digital entertainment content across the DVI/HDMI interface. The HDCP specification provides a robust method for transmitting and receiving digital entertainment content to DVI/HDMI-compliant digital displays. High-bandwidth is usually achieved by one of two means: shielded copper wires or an optical fiber link. The first generation of HDCP transmission systems were realized by parallel shielded copper wire cables. Due to bandwidth limits on optical fiber links, multiple parallel optical fibers have been traditionally used for HDCP applications. A four-fiber module has three forward channels and one backward channel. It requires four light sources, four fiber links, and four receivers. A two-fiber module has one forward channel and one backward channel. It requires two light sources, two fiber links, and two receivers. For longer distance applications, such as 100 to 1000 meters, the cost of buying and maintaining multiple fibers is considered expensive.
If a single fiber bidirectional optical transmission system is used, waveguide combiners and splitters require a high precision assembly in the range of ±5 um for multimode application using conventional waveguide layouts. The need for high precision in manufacture increases production costs and lowers productivity.